1. Field of the Invention
The present invention relates to an apparatus for the distribution of pulverulent solids onto the surfaces of a glass substrate, in order to coat it with thin layers giving it optical, thermal and/or electrical properties. This apparatus more particularly makes it possible to deposit thin layers or films by so-called pyrolysis process consisting of spraying said pulverulent solids suspended in a gas in the direction of a substrate heated to a high temperature, so that they decompose into oxides on contact therewith. The substrate can be in the form of a continuous float glass ribbon. The distribution apparatus has a cavity terminating as a distribution slot in the vicinity of the ribbon and positioned transversely to its movement axis.
2. Discussion of the Related Art
In order to obtain thin, homogenous and regular layers, it is necessary for the distribution apparatus to ensure a good powder-gas homogenization and a good distribution of said mixture over the entire length of the distribution slot.
Two apparatuses meet these criteria. Thus, EP-B-125 153 discloses a pulverulent solid distribution nozzle whose length can correspond to the width of the substrate to be treated and which has a longitudinal cavity whose walls regularly converge in the direction of the substrate to be treated. In its upper part, the nozzle has a plate forming a cover for the cavity. The plate has an opening permitting the supply of powder suspended in a gas, called the primary gas, by separate supply pipes. The powder supply pipes are located in said opening over the entire length of the nozzle and are, e.g., reciprocally spaced by approximately 50 mm, so as to introduce powder over the entire length of the cavity. Said supply pipes are not tightly fixed in said opening, which makes it possible for gas or more generally air from the ambient atmosphere to enter the cavity of the nozzle. The longitudinal walls of the cavity and the plate forming the cover define, in the upper part of the nozzle, two slots which extend over the entire nozzle length and by which are introduced pressurized supplementary gases known as secondary gases. The secondary gas is injected at a speed well above that of the primary gas in which the pulverulent product is suspended. This high speed makes it possible to accelerate the displacement movement of the pulverulent product towards the outlet slot of the nozzle and aids the uniform distribution of the injected gas flow over the entire length of the nozzle. Thus, the secondary gas also entrains the gas or air of the ambient atmosphere (induced air or gas) thus permitting the formation of turbulence, which aids the homogenization of the gas-pulverulent product mixture.
U.S. Pat. No. 5,005,769 also discloses a distribution apparatus having, as hereinbefore, two walls defining a strip-like cavity, provided in the upper part with an orifice in which are located a line of injectors for a pulverulent solid suspended in a gas, and a gas (and in particular ambient air) intake adjacent to said injectors. The cavity is also equipped with pressurized gas injection means having a chamber supplied with pressurized gas and issuing into the cavity by an opening arranged so as to inject the gas in the direction of the substrate, substantially parallel to the wall of the cavity adjacent to said opening. The opening is preferably constituted by a plurality of apertures having an axis substantially parallel to the wall of the cavity adjacent thereto.
Although both of the aforesaid apparatus types are satisfactory, each of them is only able to deposit a single layer, whereas it is an ever more frequent occurrence to provide glass substrates with a stack of plural thin layers. Thus, if it is wished to deposit several layer successively, e.g., on a continuous glass ribbon, using a pulverulent solid pyrolysis method, the only solution up to now has been to juxtapose several apparatuses along the ribbon movement axis, which leads to numerous inconveniences.
Thus, in a float glass installation, deposits by powder pyrolysis are usually performed on the glass ribbon between it leaving the float glass enclosure and its entry in the lehr, i.e., a zone often having very restricted dimensions. If it is wished to position several distribution apparatuses successively above the glass ribbon, this can lead to considerable difficulties and may even be impossible due to their dimensions.
Even when space is adequate, having successively depositing on the glass ribbon coatings at different locations of the float glass installation may make it necessary to carry out a glass reheating operation between two depositions, which makes the design of the installation more complicated.